Self-stabilizing combustion apparatus and method



June 1965 J. D. NESBITT 3,187,799

SELF-S TAB ILI Z ING CQMBUS TION APPARATUS AND METHOD Filed April 11. 1961 4 Sheets-Sheet l |-(TO FURNACE TEMPERATURE DETECTOR) l I FURNACE 2 TE MPERATURE CONTROLLER INVENTOR. JOHN D. NESBITT ATTORNEY June 1965 J. D. NESBITT 3,187,799

SELF-STABILIZING COMBUSTION APPARATUS AND METHOD Filed April 11. 1961 4 Sheets-Sheet 2 INVENTOR. JOHN D. NESBITT ATTORNEY J. D. NESBlTT SELF-S TAB ILI Z ING COMBUS TI ON APPARATUS AND METHOD 4 Sheets-Sheet 5 Filed April 11 1961 INVENTOR.

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J. D. NESBITT 3,187,799

SELF-STABILIZING COMBUSTION APPARATUS AND METHOD June 8, 1965 4 Sheets-Sheet 4 Filed April 11. 1961 IN VEN TOR.

JOHN D. NESBITT ATTORNEY United States Patent 3,187,799 SELF-STABILIZENG QGMBUS'IFEQN APPARATUS AND li/E'EHQD .lohn D. Neshitt, Toledo, flhio, assignor to Midiaud-Ross Qorporation, Toledo, Ghio, a corporation of Ghio Filed Apr. 11, 1%1, Ser. No. 102,316 4 Claims. (Cl. 158-109) This application is a continuation-in-part of my copending application, Serial No. 808,161, filed April 22, 1959, now abandoned.

This invention relates to a system for stabilizing the combustible reaction of streams of fuel and air in various types of combustion apparatus. More particularly, the invention relates to the method of and apparatus for making variou types of combustion equipment self-stabilizing.

The stabilization of the combustible reactions promoted by various types of industrial combustion apparatus is frequently accomplished by means of a separate combustion system, normally of the pre-mix type, used as a piloting system. The use of a separate piloting system to provide flame stability for a principal combustion system has a number of undesirable features among which are the complication of the structure of the burners of the principal combustion system to make them suitable to receive a pilot burner, complication of the piping required to pipe the overall system, and, in the case of a pre-mix piloting system, certain well recognized safety hazards.

it is, therefore, an object of my invention to overcome the dependency of prior art combustion systems on separate piloting systems for proper flame stability. It is a further object of this invention to accomplish the aforesaid object by providing self-stabilizing combustion apparatus and method.

For further consideration of what I believe to be novel and my invention, attention is directed to the preferred form of my invention as disclosed in the following portion of the specification, the appended claims, and the accompanying drawing.

FIG. 1 illustrates an elevational view, in section, of a burner embodying the present invention.

FIG. 2 illustrates a view taken on line 2-2 of FIG. 1.

FIG. 3 illustrates an elevational View, in section, of a burner embodying the present invention, the burner being specifically adapted to fire into an immersion heating tube.

FIG. 4 illustrates an elevational view of a radiant heat ing tube of the hairpin type having a burner embodying the present invention.

FIG. 5 illustrates an elevational view, in section, of an alternative burner construction embodying the present invention.

FIG. 6 illustrates a view taken on line 6-6 of FIG. 5.

FIG. 7 illustrates an elevational view, partially in section, of a single pass radiant tube having a burner of alternative construction embodying the present invention.

FIG. 8 illustrates a view of the burner of FIG. 7 taken on line 8-8.

FIG. 9 illustrates a view taken on line 9-9 of FIG. 8.

Referring in more detail to the drawing and in particular to FIGS. 1 and 2 a burner 10 is hown thereat installed anima s in a furnace wall. A typical application for this burner is in a low temperature tempering furnace. Burner 10 comprises a tunnel block 11 attached to burner body 12. Tunnel block 11 is of refractory composition and square configuration with a cylindrical tunnel chamber 13 extending longitudinally therethrough. The burner body 12, which is generally made of cast steel, is adapted to be installed in a refractory lined furnace wall 14. Burner body 12 is attached to metallic casing 15 of furnace wall 14 by means of studs 16 affixed to casing 15 and extending through holes 17 in burner body 12. Nuts 18 threaded on studs 16 securely hold the burner body to the casing, and the studs are so positioned that the body is properly aligned with respect to cylindrical tunnel chamber 13.

Burner body 12 has backplate 19 attached thereto by means of studs 21 affixed to body 12 and extending through holes 22 in plate 19. Nuts 23 threaded on studs 21 securely hold the backplate to the burner body.

Disposed within the burner body 12 is wall means forming a substantially cylindrical combustion chamber 24 axially aligned with tunnel chamber 13 and welded to backplate 19. Combustion chamber 24 has an outwardly expanding or tapered section 25 at its exit end for approximately /3 of the total chamber length. The tapered section expands from the cylindrical portion 26 of cham ber 24 to approximately the internal diameter of tunnel chamber 13. The tapered section is used merely to provide smooth expansion of the gases from cylindrical portion 26 to the tunnel chamber. In a larger capacity burner, the same burner body 12 can be used with a larger cylindrical combustion chamber equal in diameter to the tunnel chamber diameter and having no tapered portion. For example, the combustion chamber 124 of the burner in FIG. 3 i shown as a straight cylindrical casting.

A fuel pipe 27 is welded to backplate 19 flush with the inside face thereof and in substantially axial alignment with combustion chamber 24 and tunnel chamber 13. Pipe 27 is supplied fuel from a source, not shown, through lines 28, 29 and 31 the latter two lines containing valves 32 and 33 respectively. Backplate 19 is also provided' with two tapped holes 34 and 35 into which pipe plugs 36 and 37 are inserted. Holes 34 and 35 are located equidistant from the axis of and within the combustion chamber when the latter is Welded to the backplate. The burner can be ignited through one of the holes 34 and 35 by an electric or fuel torch. As will be explained later, the combustion chamber will normally be under positive pressure, and unless the burner is ignited at throttled air flow, it may be difficult to ignite because of outflow through the hole. For gaseous fuel operation, the preferred form of ignition will normally be an electric spark inserted into one of the holes 34 and 35 in place of pipe plug 36 or 37.

A commercially available flame rod safety device may be placed in the other of the holes 34 and 35 in place of pipe plug 36 or 37 to shut oif a valve in line 28 should the flame in chamber 24 become extinguished.

Air inlet pipes 38 and 39, FIG. 2, are welded tangent to the internal diameter of combustion chamber 24 adjacent backplate 19. Pipes 38 and 39 are directed perpendicularly to the axis of chamber 24 and are normally spaced from the backplate 19 a short distance such as to /2" and, as shown in FIG. 2, they are spaced 180 apart and attached to the combustion chamber in a manner to introduce the air in the same direction, in this case counterclockwise. Inlet pipes 38 and 39 are shown entering combustion chamber 24 adjacent holes 34' and 35 in backplate 19. They are shown in this manner for convenience and could be located spaced 90 from their present location, or under some circumstances it may be desirable to supply four inlet pipes 90 apart. Inlet pipes 38 and 39 must belong enough in relation to their internal diameter to provide a traight air flow path. A length to inside diameter ratio of at least 2 to 1 has proven satisfactory. By virtue of the perpendicular disposition of inlet pipes 38 and 39 with respect to the axis chamber 24 the air admitted therethrough will have substantially no component of motion parallel to the axis of chamber 24.

Additional air is admitted to combustion chamber 24 by a plurality of apertures 41 in the chamber wall means downstream of the tangential air inlet pipes 38 and 39. The size and location of apertures 41 are such as to maintain combustion of the fuel stream in combustion chamber 24 at a maximum rate without flame quenching. A convenient pattern for spacing apertures 41 to obtain radial entry of air is in a plurality of axially spaced circumferential stages. The burner of FIG. 1 shows four of these stages downstream of the tangential air inlet pipes 38' and 39. The first three stages are in cylindrical portion 26 of the combustion chamber, and each stage contains four apertures circumferentially spaced 90 apart. The fourth stage is located in outwardly tapered section 25, and it contains eight apertures circumferentially spaced 45 apart.

Air entering each aperture 41 will produce a back eddy current which will promote stable burning with maximum mixing. As previously stated, the size and spacing of apertures 41 is such as to maintain combustion at the maximum possible rate without flame quenching. Flame quenching is indicated by the presence of intermediate combustion products. The presence ofintermediate combustion products can be qualitatively detected, even in extremely minute quantities, by the characteristic pungent odor of the aldehydes formed. Once flame quenching is known to exist by the detection of aldehyde odors, the extent of the flame quenching can be becoming inoperative, and the general maintenance of the burner is greatly increased.

The preferred air pressure drop is 1.5 to 3.5" w.c. with operation at approximately 2" w.c. being standard. Increasing the pressure beyond 3.5" w.c. results in flame quenching and the consequent production of aldehydes.

Fuel is supplied to fuel pipe 27 at 0 to 1" w.c. pressure. Under normal excess air operation the air flow is maintained constant, and the fuel is cut back as heat demand decreases. Because of the extremely wide range of excess air that may be used, any of the common control systems may be used. With the valve arrangement of FIG. 1, a simple high-low control system can be used. When the burner is firing at full capacity, both valves 32 and 33 will be open to supply fuel from line 28 through lines 29 and 31. When heat demand decreases, a simple temperature controller 30 can be used to close valve 33, and only a small percentage of maximum fuel flow, for example, 3 to 5% will be supplied from line 28 through line 29 and open valve 32. A proportional or modulating control system can also be used wherein one of the valves 32 and 33, shown in FIG. 1 as valve 33, would be a motor driven valve throttled by the temperature controller 30 an amount which is proportional to the deviation between set point or desired furnace temperature and actual furnace temperature.

Excess air burners of this type can be commonly built with capacities ranging from 300,000 to 3,000,000 B.t u./ hr. with a corresponding turndown ratio (maximum to minimum fuel flow) of from 30/1 to 100/1. The prior patent art indicates that the heating capacity of luminous or long flame burners ranges up to approximately a maxievaluated quantitatively by; measurement of carbon monoxide content in the combustion gases. In this manner, the optimum aperture arrangement can be accurately determined for burners of different capacity.

The space between. burner body 12 and combustion chamber 24 defines an annular air chamber 42. Air is supplied to thischamber by a blower and piping, not shown, to flange portion 43 of burner body 13., Air is then properly distributed between tangential air inlet pipes 38 and 39 and radial apertures 41 by their relative areas.

In excess air operation of the burner, a small percenage of the total air supplied to air chamber 42 is introduced to combustion chamber 24 through tangential air inlet pipes 38 and 39 to form a spinning air stream circumposing an axially flowing fuel stream emitted to the chamber through fuel pipe 27. The combustible mixture of fuel and air formed at the interface of the spinning air stream and the axially flowing fuel stream is ignited through one of the apertures 34 and 35 in'backplate 19. to establish a spinning, slow mixing, stable flame adjacent the gas nozzle. This spinning flame, in effect, establishes an extremely stable pilot for the balance of the fuel and air. 7

The preferred amount of air emitted through the tangential air inlet pipes is approximately 57.5%, with 4-10% of the total air being acceptable. If too little of the total air is admitted to the tangential air inlet pipes, for example, less than 4%, the air will pull out in a parabola along the gas stream to produce an unstable mum of 70,000 B.t.u. per hour per cubic foot of combustion space; whereas, the burner of the present invention has a heating capacity of 1,000,000 B.t.u. per hour per cubic foot of combustion space.

Burner 110, shown in FIG. 3, is a modification of burner 10 and is particularly designed for heating immersion tubes. The similarity of elements of the embodiments of FIGS. 3 through 9 to the embodiment of FIGS. 1 and 2 is indicated by identifying them with a three digit numeral whose. last two digits are the same as the two digits of the numeral used to identify the corresponding element of the embodiment of FIGS. 1 and 2.

In heating sealed immersion tubes, it is desirable to compromise between the rapid mixing, high capacity burner 10 of FIG. 1 and the prior art long flame burner. If burner 10 were used without modification for this application, a hot spot would result adjacent the point where the burner is joined to the tube because combustion is rapid and is completed close to the exit of the combustion chamber even when firing at maximum capacity. It is desirable to complete combustion uniformly along the length of the tube so that the tube becomes uniformly heated.

Burner of FIG. 3 is shown attached to immersion tube 144 in the same manner as burner 10 is attached to metallic furnace casing 15. The basic difference between the two burners is that the air supplied to combustion chamber 24 through radial apertures 41 in burner 10 is supplied in the burner 110 of FIG. 3 in part to the combustion chamber 124 through apertures 141 and in part directly to immersion tube 144 through spin vanes 145 circumposing the combustion chamber adjacent its outlet end.

Spin vanes 145 are attached to flange member 146 over which immersion tube 144 is slipped for mounting to burner body 112. Spin vanes 145 thus occupy the annular space between flange member 146 and combustion chamber 1-24. Vanes 145 are attached to flange member 1146 at some angle, shown nominally as 45, to the axis of flange member 146 and combustion chamber 124 to cause the air to spin a desired amount. The spacing between vanes is designed to proportion the ratio of aperture 141 area to the effective annular area of the spin vane assembly to thus proportion the ratio of air admitted radially to the combustion chamber and the amount admitted to immersion tube 144 through spin vanes 145.

Spin vanes 145 impart a spiral motion to the air passing through them into immersion tube 144 so that this air'spins around the axially flowing fuel and products of combustion stream issuing from combustion chamber 124, and the spinning air also travels axially down tube 144. long flame which travels the length of the immersion tube. The spiralling air eliminates hot spots and produces a uniform temperature distribution over the length of the immersiontube by the combined effect of lengthening the flame and providing a spiralling layer of air adjacent the inside wall of the tube through which the heat must pass. The amount of air which passes through the spin vanes is normally regulated at 70-75% of the total air.

FIG. 4 shows another modification of the burner adapted to fire into a commonly used hair-pin type radiant tube 247. Burner 21% is the same as burner lltl. of FIG. 3 having a spin vane assembly, except that a burner body 112 or air housing is not placed around the combustion chamber 224. Air is supplied to one of the tangential air inlet pipes 239 under pressure to provide a spinning, slow mixing, stable flame at the point of entry of the fuel through pipe 227 to combustion chamber 224.

An eductor 248 is coupled to the exhaust end of radiant.

tube 247 to produce a draft or suction through the tube to cause air at atmospheric pressure to flow into combustion chamber 224 through radial apertures 241 and through the spin vanes into tube 247. The draft also pulls in the fuel thr-ough pipe 227 which is in substantially axial alignment to combustion chamber 224. Additional air is drawn into tangential air inlet 23% as the firing rate is increased by increasing the draft produced by eductor 248; this air adds to the spinning air admitted under pressure to air inlet 239. Burner 210 produces a long flame in radiant tube 247, and it operates in essentially the same manner as burner 113 except that the air is drawn into the burner by an eductor at the exhaust end of the tube instead of being supplied under pressure to the burner.

The burner 31%) illustrated in FIGS. 5 and 6 may be contrasted to burner 13 of FIGS. 1 and 2 by the fact that it is essentially a long-flame burner. Such a burner, which may be operated on either the excess air principle or as a proportioning burner, or on some combination of the two, is well suited for heating relatively high temperature furnace chambers (say over 1200 P.) where there is little danger of quenching a long flame. The burner 31% comprises tunnel block 311 attached to burner body 312 which is shown constructed of a weldment but which may also be constructed, at least partially, of casting in the same manner as the burner of FIGS. 1 and 2. Burner body 312 is attached .to metallic casing 315 of furnace wall 314 by means of studs 316 aifixed to casing 315 and extending through holes 317 in burner body 312. Nuts 318 threaded on studs 316 securely hold the burner body to the casing, and the studs are so positioned that the body is properly aligned with respect to cylindrical tunnel chamber 313.

Burner body 312 has backplate 319 attached thereto by means of continuous weld 351. Disposed within burner body 312 are wall means forming a substantially cylindrical combustion chamber 324 axially aligned'with tunnel chamber 313 and welded to backplate 319. A fuel inlet pipe 327 is inserted through an aperture 352 in back- The spiralling air tends to produce a slow mixing plate 319. and is affixed in place by continuous weld 353 in such a manner that the outlet end 327a of fuel inlet 327 is, for reasons which are to be indicated later, located V at a distance somewhat downstream, with respect to the direction of fuel flow from backplate 319. Pipe 327 is A portion of the combustion air, preferably from 410% of the amount required for stoiohiometric combustion of the fuel stream added through inlet 327, is admitted tangentially to combustion chamber 324 from annular air chamber 342, defined by burnerbody 312 and combustion chamber 324, by means of air inlet conduits 338 and 339. Conduits 333 and 339 are defined on three sides by channel-shaped members 354 and 355, which are adapted to be inserted in milled slots (not shown). in the end of combustion chamber 324 and on the fourth side by a portion of baclrplate 313. Air inlet conduit 338 and 333 must be located very closely adjacent backpl'ate 319, a feature which will inhere in the illustrated mode of construction, and the axes thereof must be perpendicular to the axis of combustion chamber 324.

Burner 319 diflers primarily from burner 19 in that only a very small portion of the required combustion air is added to combustion chamber 324 Whereas all of the required combustion air is added to combustion chamber 24 .of FIG 1. Thus burner 31d of FIGS. 5 and 6 incorporates the spin stabilizing feature of burner It of FIGS. 1 and 2 but it does not utilize the radial addition of the main or secondary air stream. In burner 31% the main air stream is combined with the unburned fuel stream passing from combustion chamber 324 in a region downstream thereof, he in tunnel 313. This is accom: plished by mounting body 312 to furnace casing 315 in such a fashion that annular chamber 342, is in fluid com: munication with tunnel block 313. Thus, air will pass from chamber 342 into tunnel block 313 circumposing the fuel flowing from combustion chamber 324. To provide for rapid mixing (and hence rapid combustion) in tunnel block 313 of the air stream from chamber 342 and the fuel stream from tube 327 an orifice plate 356 is inserted in the annular space defined by the inside diameter of burner body 312 and the outside diameter of combustion chamber 324. The high degree turbulence imparted to the air stream by virtue of sudden re-expansion occurring downstream of orifice plate ass greatly increases the rate of intermixing of the fuel and air streams in tunnel 313 over the rate of intermixing which would occur through natural turbulence.

Although it would be possible to construct orifice plate 336 as a simple annular plate attached either to the inher surface of burner body 312 or, preferably, to the outer surface of combustion chamber 324 (ie with an inner diameter slightly greater than the outer diameter of chamber 324 and an outer diameter substantially less than the inner diameter of burner body 312) it is preferred to use a more'cornplex construction for reasons to be explained later. The more complex construction comprises an annular plate which would substantially block the annular space between burner body 312 and combustion tube but for a plurality of radial slots 357 formed around the outerperiphery thereof. Such a construction, as has been found by experimentation, reduces to a minimum the suction imposed on the outlet end of chamber 324 by the turbulent motion of the air stream downstream thereof. An excessive suction in this region will undesirably tend to draw the flame front from its stabilized position within combustion chamber 324.

The fact that there are conditions downstream of combustion chamber 324 which may create a slight suction or negative pressure therein, whereas combustion chamber 24 of burner 10 of FIGS. 1 and 2 normally operates at positive pressure by virtue of the staged radial admission of secondary air through ports 41, leads to another important structural distinction between burner 10 and burner 310. In burner 10 the end of fuel pipe 27 termi-.

spinning air, which is added to combustion chamber 324 through tangential air inlet conduits 338 and 339, forms a vortex with a concomitant vortex suction effect immediately downstream of the outlet end 327a of fuel inlet pipe 327; the vortex suction in the region of outlet end 327a tends to divert an outer annular layer of the fuel stream passing therefrom and cansesthe diverted portion to flow, in reverse in an annular layer immediately outside of the extended portion of inlet 327, toward backplate 319; the

diverted portion of the fuel stream mixes with the spinning 8. obtained in the additional passes of the multiple pass tube which greatly increase the length to diameter (L/ D) ratio of the tube. Because of the greater L/D ratio of a multiplepass radiant tube, the extremely long flame characteristic of a diffusion burner is not only tolerable but is even desirable in that it promotes more uniformheat release from all portions of the radiant tube surface. Consequently, pre-mix combustion is commonly employed only to a limited extent in prior art multiple pass radiant tube firing systems and usually only as anexpedient to overcome the poor flame stability characteristic of prior art diffusion burners.

Certain industrial furnace designs are, however, because of space limitations or other factors, not readily suited to being heated by a bank of multiple pass radiant tubes. Such furnaces can be conveniently. heated only by a pluraltiy of single-pass radiant tubes. Examples of air stream to form a spinning combustible mixture adjacent backplat e 319; the spinning combustible mixture can be readily ignited by holding a torch or match to small port 334 because of the fact that flame will pass therethrough since combustion chamber 324 is under suction; the spinning combustible mixture, when once ignited, will continue to burn forming a spinning highly stable flame front which will serve to stabilize the main combustible reaction between the uncombusted fuel stream passing from combustion chamber 324 and the main air stream passing through slotted orifice plate 356. Thus, burner 310 of FIGS. 5 and 6, like burner 10 of FIGS. 1 and 2 and burners 110 and 210 of FIGS. 3 and 4, is self-stabiliz- FIGS. 7-9 illustrate a radiant tube burner 410 embodying the self-stabilizing feature of burners 10, 110, 210and 310. Radiant tube burner 410 differs from the radiant tube burner 210 in function, by virtue of the fact that it is specifically suited to fire a single-pass radiant tube whereasburner 210 is primarily suited to fire a radiant tube with a plurality of passes such as the illustrated hairpin tube. Radiant tube burner 410 diflers further from burner 210 in that it, like the immersion tube burner 110,- is specifically adapted to be fired under pressure.

The combustion of a fuel stream within a narrow elongate radiant heating tube may be achieved either according to the principle of pre-mix combustion or according to the principle of diffusion combustion or according to some combination ofthe principles of pre-rnix combustion and diffusion combustion. Pre-mix combustion, by

definition, is the combustion of a stream of homogeneously mixed fuel and air, normally mixed in approximately stoichiometric proportions. Diffusion combustion, on the other hand, is the combustion of the combustible mixture of fuel and air which occurs by diffusion at the interface of contiguously flowing streams of fuel and air. Pre-mix combustion is normally characterized by a flame which is relatively short and highly stable whereas diffusion combustion is characterized by a flame which is quite long and relatively unstable. Some prior artisans have found it expeditions to offset these relative merits and demerits of pre-mix and diffusion combustion by combining these combustion principles into a combustion technique known as partial pre-mix partial diffusion. An example of this technique is described in US. Patent 2,873,798 to Knight which discloses a radiant tube burner of the diffusion type piloted by a cluster of pre-mix pilot burners.

Simple diffusion combustion has long been widely recognized as an ideal combustion technique for multiple-pass radiant tube elements which are commonly constructed in the shape of a U or a W. In such radiant tubes there is normally available a relatively large combustion volume when compared to the combustion volume available in single-pass radiant tubes, the additional volume being such a furnace are described in US. Patents 2,822,798 and 2,849,220. The single pass radiant tubes used to heat such furnaces are characterized by a relatively small length to diameter ratio when contrasted with the length to diameter ratios of multiple pass radiant tubes. Because of the small length to diameter ratio of single pass radiant tubes, it has heretofore not been practicable to fire such radiant tubes with conventional diffusion burners due to the excessive flame length characteristic of prior art diffusion burners. Accordingly it hasbeen the practice of prior artisans to fire such single pass radiant tubes with partial diffusion, partial pre-mix burners using a much higher degree of pre-mix combustion than was needed for mere stabilization of the diffusion combustion flame.

The use of pre-mix combustion in any radiant tube firing system creates numerous problems many of which become especially severe in single pass radiant tube firing systems which, heretofore, have required a very high tion of the radiant tube immediately downstream of the burner. This problem can be quite severe by virtue.

of the fact that this portion. of the radiantntube is normally surrounded by the thick refractory material with which the furnace is lined, such refractory tending to retard heat transfer from the shieldedportion of the radiant tube.

Burner 410 of FIGS. 7-9 isshown attached .to singlepass radiant heating tube 447 which passes through, and is adapted to deliver heat to, furnace chamber 461 which is defined by wall means 414 of refractory construction backed up by metallic casing plate 415. Radiant tube 447 is disposed vertically in chamber 461 and is supported on annular retaining plate 462 which is attached to casing plate 415 by means of studs 463 and nuts 464. Burner 410 is mounted in coaxial fluid communication with radiant tube 447 by attaching it to annular retaining plate 462, as by means of studs 465 and nuts 466. Burner 410 comprises burner body 412 and a backplate 467 aflixed thereto by means of bolts 468 and nuts 469 with a gasket471 inserted between burner body 412 and backplate 467 to seal the joint therebetween. Extending through a hole in backplate 467 is a combustionchamber 424 formed by cylindrical wall 472 and backplate 419, it being noted that combustion chamber 424 ought to be substantially coaxial with burner body 412. Extending through a hole in backplate 419 and terminating at a point somewaht downstream (with respect to the direction of fuel flow therethrough) is a fuel inlet pipe 427 which is'in substantially axial alignment with combustion chamber 424.

A stream of air comprising 1-10% of the amount of air required for stoichiometric combustion of the stream of fuel flowing through fuel inlet pipe 427 is added tangentially to combustion chamber 424 by means of air inlet pipe 438. Air inlet pipe 438 is located upstream of the outlet end 427a of fuel inlet tube 427 and is disposed with its axis perpendicular to the axis of combustion chamber 424 so that the stream of air which passes into combustion chamber 424 has substantially no component of motion parallel to the axis of combustion chamber 424. A spinning stable ring of flame can be obtained adjacent backplate 419 of burner 419 in the same manner that a stable ring of flame is obtained adjacent backplate 319 of burner 31% except that, in the case of burner 41% the flame front can sometimes be caused to shift from a region adjacent backplate 419 to a region adjacent the outlet end of combustion tube 424 due to suction on combustion tube caused by tangential admission of main air to burner body 412. The shifting of the flame front in this fashion has not been found to be particularly undesirable and the flame front will normally recede to a region adjacent the backplate when the suction on combustion tube 424 is reduced as the rate of admission of main air to burner body 412 is reduced on normal turndown. The only noteworthy aspect of the shifting flame front phenomenon is that, in instances where flame monitoring is desired, it is necessary to monitor at a point downstream of combustion chamber 424. This may be accomplished by inserting a conventional flame detecting rod (not shown) through fragmentary pipe coupling 473 attached to burned body 412 coaxially with aperture 474 and being disposed with its axis adapted to intersect the axis of combustion chamber 424 at a point downstream thereof.

Ignition of the flame stabilizing ring in combustion chamber may be accomplished by means of a spark plug (not shown) inserted through fragmentary pipe coupling 475 attached to combustion chamber 424 coaxially with aperture 476 and being disposed with its axis adapted to intercept the axis of fuel inlet pipe 427 at a point downstream thereof.

The main stream of combustion air for combusting the unburned portion of the fuel stream emerging from combustion chamber 4-24 is added tangentially by means of air inlet connection 443 to the annulus 477 formed between the outside diameter of combustion chamber 424 and the inside diameter of burner body 412. It is especially important in a burner adapted for firing a single pass radiant tube that air inlet connection be disposed with its axis substantially perpendicular to the axis of combustion chamber 424. Such a construction impaits a very rapid tight spinning motion to the stream of main combustion air as contrasted to the lazier spiraling motion imparted to the stream of main air by turning vanes 145 of burner 11%. Due to the relatively high vortex suction effect with an associated high degree of turbulence at the axis of a tightly spinning air stream the fuel stream flowing along the axis will tend to mix very rapidly with the spinning air stream. The mixing occurring in this fashion will proceed in a pattern starting from the axis outwardly to the inner periphery of radiant tube 447. Thus, the extreme outer layer of the spinning air stream will retain its autonomy for a sufficiently long period to provide for eflective high convection cooling of firing end portion 447a of radiant tube 447 which is shielded by a portion of refractory wall 414 and which, because of the limited ability of refractory Wall 414 to absorb heat therefrom, is a portion particularly susceptible of being overheated.

In constructing burner 4-19 it is important to pay careful attention to the size of annulus 477 so that it is neither too large or too small. I have found that the optimum annulus size is one that will impart a pressure drop of 45 in. -w.c. to the stream of spinning air flowing therethrough when air is being added at the maximum desired rate. A smaller annulus will impart a higher pressure drop to the air stream and this will undesirably tend to dampen the spinning motion of the air stream. A larger annulus will 10 impart a lower pressure drop to the air stream and this will undesirably reduce the rate of mixing of the spinning air stream and the axially flowing fuel stream.

The best modes known to me to carry out this invention have been described in terms sufficiently full, clear, concise, and exact as to enable any person skilled in the art to practice the invention. However, it is to be understood that various modifications of the above will be readily ap parent to a' skilled artisan without departing from the scope of the invention which is defined only by the appends ed claims.

I claim:

i. Self-stabilizing burner apparatus comprising, in combination: wall means forming a substantially cylindrical, combustion chamber having an inlet end and an exit end; a fuel pipe for introducing a stream of fuel substantially axially into said combustion chamber; air inlet means entering said chamber adjacent said inlet end and tangent to the inside of said chamber for introducing 410% of a total amount of air supplied to said chamber in a spinning stream circumposing said fuel stream, the axis of said air inlet means being directed parallel to a plane which is disposed perpendicularly to the axis of said chamher; an aperture in said inlet end of said wall means suitable for igniting the air and fuel at the interface of said axially flowing fuel stream and said spinning air stream to form a stable spinning pilot flame circumposing said gas stream adjacent said inlet end; and means for supplying the balance of said total air radially to said chamber downstream of said spinning pilot flame.

2. Self-stabilizing burner apparatus adapted to heat a furnace comprising in combination: wall means forming a substantially cylindrical combustion chamber having an inlet and exit end; pipe means for introducing a stream of fuel substantially axially into said chamber; a valve in said pipe means; control means responsive to the temperature in said furnace for opening and closing said valve an amount proportional to the deviation between measured and desired furnace temperature; means for introducing a small percentage of a constant amount of air supplied to said chamber tangentially to said chamber adjacent said inlet end and disposed parallel to a plane which is directed perpendicularly to the axis of said chamber to form a spinning stream of air circumposing said fuel stream, said Wall means having an aperture in said inlet end suitable for igniting the air and fuel at the interface of said axially flowing fuel stream and said spinning air stream to form a stable spinning pilot flame circumposing said gas stream adjacent said inlet end; and means for supplying the balance of said constant amount of air to said chamber in a plurality of radial stages downstream of said spinning pilot flame in a manner so that as the valve is closed by said control means and the flame recedes in said combustion chamber toward the inlet end thereof, the flame front location and air admission are in balance.

3. The method of operating self-stabilizing burner apparatus having wall means forming a substantially cylindrical combustion chamber with an inlet end and an exit end, said method comprising the steps of: introducing a stream of fuel to the chamber through the inlet end substantially parallel to the axis of the chamber; introducing a primary supply of air comprising 410% of a total supply of air substantially tangentially to the chamber and parallel to a plane disposed perpendicularly to the axis thereof, said primary supply of air being introduced to the chamber in at least one stream at a region adjacent the inlet end to form a spinning stream of air circumposing the fuel stream; igniting the mixture of fuel and air which forms at the interface of the axially flowing fuel stream and the spinning stream of air to form a stable flame retention ring in said chamber; and mixing the remainder of the total air supply with the stream of fuel to sustain the combustion thereof by introducing at least a substantial portion thereof radially to the combustion 1 1' chamber downstream of the region of introduction of the primary supply of air.

4. The method according to claim 3 wherein substantially all the remainderof the total air supply is introduced to the combustion chamber in a plurality of axially spaced circumferential stages in amounts sufficient to sustain combustion of the fuel at a maximum rate without flame quenching.

References Cited by'the Examiner UNITED STATES PATENTS Oldenkamp. Burg 110-28 te Nuyl 1581.5 X Jensen.

Johnson 'Mock.

FOREIGN PATENTS JAMES W. WESTHAVER, Primary Examiner.

PERCY L. PATRICK, Examiner. 

1. SELF-STABILIZING BURNER APPARATUS COMPRISING, IN COMBINATION: WALL MEANS FORMING A SUBSTANTIALLY CYLINDRICAL, COMBUSTION CHAMBER HAVING AN INLET END AND AN EXIT END; A FUEL PIPE FOR INTRODUCING A STREAM OF FUEL SUBSTANTIALLY AXIALLY INTO SAID COMBUSTION CHAMBER; AIR INLET MEANS ENTERING SAID CHAMBER ADJACENT SAID INLET END AND TANGENT TO THE INSIDE OF SAID CHAMBER FOR INTRODUCING 4-10% OF A TOTAL AMOUNT OF AIR SUPPLIED TO SAID CHAMBER IN A SPINNING STREAM CIRCUMPOSING SAID FUEL STREAM, THE AXIS OF SAID AIR INLET MEANS BEING DIRECTED PARALLEL TO A PLANE WHICH IS DISPOSED PERPENDICULARLY TO THE AXIS OF SAID CHAMBER; AN APERTURE IN SAID INLET END OF SAID WALL MEANS SUITABLE FOR IGNITING THE AIR AND FUEL AT THE INTERFACE OF SAID AXIALLY FLOWING FUEL STREAM AND SAID SPINNING AIR STREAM TO FORM A STABLE SPINNING PILOT FLAME CIRCUMPOSING SAID GAS STEAM ADJACENT SAID INLET END; AND MEANS FOR SUPPLYING THE BALANCE OF SAID TOTAL AIR RADIALLY TO SAID CHAMBER DOWNSTREAM OF SAID SPINNING PILOT FLAME. 